Heat flow device

ABSTRACT

A device comprises equipment ( 101 ) with a heat source, a cold part ( 102 ) relative to the equipment, and a thermal conductor element ( 103 ) capable of conducting the heat from the equipment to the cold part. The element ( 103 ) is such that, under certain thermal conditions above a given thermal condition, the equipment and the cold part are essentially thermally isolated.

The invention relates to a heat-flow device.

In such a device it is sought to evacuate the thermal energy (or heat)dissipated in an equipment item by a heat source of any kind (such as anelectrical circuit or an electronic component).

This is traditionally achieved by connecting the equipment item, bymeans of a heat-conducting member, to a relatively colder part, whichacts as a cold source.

Thus an amount of heat flows across the conductive member, with a powerinversely proportional to the thermal resistance thereof, thus making itpossible to evacuate at least part of the heat generated within theequipment item and thus to avoid overheating it.

US Patent Application 2003/0196787, for example, uses this technique andalso proposes, for reasons related to the operation of the equipmentitem, to reduce such evacuation of heat at low temperature.

The inventors have noted that these solutions could present risks inpractice, especially when the part constituting the cold source is notadapted to all conditions of temperature and/or of dissipated thermalpower, as is the case, for example, when this cold part is formed from amaterial that is combustible or sensitive to temperature elevations.

In order to avoid such problems, the invention proposes a devicecomprising an equipment item with a heat source, a part relativelycolder than the equipment item and a member capable of transmitting theheat (especially by conduction) from the equipment item to the coldpart, characterized in that the member is such that, under certainthermal conditions situated above a given thermal condition, theequipment item and the cold part are substantially insulated thermally.

In this way the heat generated within the equipment item is no longertransmitted to the cold part when these thermal conditions (for example,of temperature or of thermal power across the member) are encountered,or in other words when the given thermal condition is exceeded, andoverheating of the said cold part is avoided.

The equipment item and the cold part may additionally be separatedsubstantially by a gas screen, at least under the said thermalconditions, in order that the transmission of electrical phenomena (suchas electrical arcs), especially the propagation of electrical arcs fromthe equipment item to the cold source, can also be avoided under theseconditions: in this case, the equipment item and the cold part areeffectively insulated electrically.

In practice, the element comprises, for example, a good heat conductoroutside the said thermal conditions (or in other words, beyond the giventhermal condition).

According to one conceivable embodiment, the member is such that itsthermal resistance is capable of increasing under the said thermalconditions, in such a way that the member becomes substantiallyinsulating. In this way the thermal insulation of the equipment item andof the cold source is made possible by the modification of thethermal-conduction properties of the member.

According to one possible solution, the member comprises at least onecomponent whose change of state (for example from the liquid state tothe gas state) under the said thermal conditions causes an increase ofthe said thermal resistance. In this case, advantage is taken of theincrease in thermal resistance generally associated with such a changeof state. The component may then form the said screen after the saidchange of state, which is a practical way of obtaining this screen.

According to another conceivable embodiment, the member is configured tolose contact with the equipment item or the cold part under the saidthermal conditions. In this case it is the breaking of contact betweenthe different components that causes the interruption of the heat pathbetween the equipment item and the cold part.

The member in this case comprises, for example, at least one componentwhose change of state under the said thermal conditions causes the saidloss of contact.

In this context it is possible to provide that the said componentparticipates in conduction from the equipment item to the cold partoutside the said thermal conditions, and disappears due to its change ofstate under the said thermal conditions, thus substantially insulatingthe equipment item and the cold part.

According to another approach, which may be combined if applicable withthe foregoing, the change of a mechanical property of the componentduring its change of state may lead to a movement of part of the member,thus causing the said loss of contact.

In this case also, the member may be configured in such a way that thechange of state of the component makes it possible to form the said gasscreen. The change of state then makes it possible not only to interruptthe thermal path but also to prevent the propagation of electricalphenomena.

In this context the change of state may be a transition from the solidstate to the liquid state or a transition from the liquid state to thegas state.

The equipment may be a fuel pump and the cold part a liquid fuel, forexample in an aircraft; the invention is particularly interesting inthis context, although it naturally has numerous other applications,such as protection against overheating of members of heat sinks that aresensitive to temperature elevations, such as carbon structures.

The arrangements proposed hereinabove, some of which are optional, thusmake it possible in particular to evacuate the heat produced by theequipment items, such as electronic components as in the case of fuelpumps, while avoiding overheating of the heat sink (such as the fuel) aswell as propagation of electrical arcs from the equipment items to thissink.

The invention also proposes an aircraft equipped with such a device.

Other characteristics and advantages of the invention will becomeevident in light of the description hereinafter with reference to theattached drawings, wherein:

FIGS. 1A to 1C represent a first exemplary embodiment of the invention;

FIGS. 2A to 2C represent a second exemplary embodiment of the invention;

FIGS. 2D to 2F represent a variant of the second example presented inFIGS. 2A to 2C;

FIGS. 3A to 3C represent a third exemplary embodiment of the invention;

FIGS. 4A to 4C represent a fourth exemplary embodiment of the invention;

FIG. 1A represents a first exemplary embodiment of the invention undernormal operating conditions.

In this example, a hot plate 101 comprising a heat source (notillustrated) is connected to a cold plate 102 (such as a structural partof the device) by means of a material 103 that is solid at the nominaltemperature T_(nominal) corresponding to normal operation.

Material 103 is a heat conductor, and its thermal resistanceR_(material) is therefore relatively low. Thus the heat generated by theheat source within hot plate 101 is evacuated under normal operatingconditions across material 103 to cold plate 102, which acts as a heatsink or cold source.

Material 103 is also chosen such that its melting temperatureT_(melting) is lower than or equal to the desired maximum operatingtemperature T_(max). Such a maximum temperature may be desired, forexample, to avoid degradation of cold plate 102 or other negativeconsequences, such as, for example, a risk of fire when the cold plateis made in the form of a combustible material, such as the fuel of anaircraft.

Thus, as represented in FIG. 1B, when the temperature T of material 103attains the melting temperature T_(melting) of material 103, for exampledue to a departure from normal operating conditions, the said materialchanges state: material 103 passes from the solid state to the liquidstate (represented by reference 103′ in FIG. 1B), which leads to itsdisappearance (in this case its flow via appropriate means) from itsinitial position in contact with hot plate 101 and cold plate 102.

Because of this fact, when the temperature between plates 101, 102 ishigher than the desired maximum temperature T_(max), hot plate 101 andcold plate 102 are no longer connected by the material but are separatedby an air screen 106, whose thermal resistance R_(air) is very muchgreater than that of the material R_(material), as represented in FIG.1C.

Cold plate 102 is then thermally insulated from hot plate 101 by virtueof air screen 106 separating them; this screen also acts as anelectrical insulator, which also makes it possible to preventtransmission of electrical energy (for example, in the form ofelectrical arcs) from the hot plate to cold plate 102. This latteradvantage is particularly interesting in the case in which hot plate 101is provided with an electrical or electronic equipment item whosepotential malfunctions could prove dangerous to cold plate 102,especially when this has attained a temperature above the desiredmaximum temperature T_(max).

Wax is used, for example, as material 103, since its thermal propertiespermit heat conduction clearly greater than that permitted by thethermal resistance of air 106.

FIG. 2A represents a second exemplary embodiment of the invention undernormal operating conditions, that is, for example, at an operatingtemperature T_(nominal) clearly lower than a desired maximumtemperature.

In this example, an equipment item 201 comprising a heat source issituated at a distance from a cold plate 202 and is consequentlyseparated from it by an air screen 206. Furthermore, equipment item 201is connected to cold plate 202 by means of a heat drain 203 formed in amaterial that is a good heat conductor (that is having low thermalresistance) and that therefore extends partly into the space formed byair screen 206.

Heat drain 203 is maintained in contact with cold plate 202 byinterposition of a bonding material 204 in solid state between a part ofequipment item 201 and conducting drain 203. Furthermore, a compressionspring 205 is interposed between drain 203 and cold plate 202, spring205 being compressed when drain 203 is in contact with cold plate 202.

Drain 203 is connected to equipment 201, on the one hand across bondingmaterial 204 and on the other hand directly at parts of equipment item201 other than those receiving bonding material 204, for example at aside wall 208 of equipment item 201.

When the temperature in bonding material 204 rises beyond the normaloperating conditions and attains the melting temperature T_(melting) ofbonding material 204, the latter passes from the solid state to theliquid state (as represented in FIG. 2B, in which the bonding materialin liquid state is represented by reference 204′), and flows away fromthe device via appropriate means.

Because of this fact, drain 203 is no longer maintained in contact withcold plate 202 but instead is moved away under the action of spring 205.Because of the displacement of drain 203 and its loss of contact withcold plate 202, equipment item 201 and cold plate 202 are separated bythe thickness (or screen) of air 206, except for spring 205, whosethermal conductivity is negligible, and these two members are thereforesubstantially insulated by means of air screen 206, as represented inFIG. 2C.

FIG. 2D represents a variant, under normal operating conditions, of thesecond example just described.

As for the second example described in the foregoing, an equipment item211 comprising a heat source is situated at a distance from a cold plate212 and consequently separated therefrom by an air screen 216.Furthermore, equipment item 211 is connected to cold plate 212 by meansof a heat drain 213 formed in a material that has low thermal resistanceand that therefore extends partly into the space formed by air screen216.

According to this variant, however, heat drain 213 is maintained bracedagainst cold plate 212 by means of a solid block 214 interposed betweenconducting drain 213 and a structural part 210. Furthermore, as in thesecond example, a compression spring 215 is interposed between drain 213and cold plate 212, spring 215 being compressed when drain 213 is incontact with cold plate 212 because of the presence of solid block 214.

Thus, according to the present variant, solid block 214 does notnecessarily participate in the flow of heat.

When the temperature in solid block 214 rises beyond the normaloperating conditions and attains the melting temperature T_(melting) ofthe material constituting block 214, this passes from the solid state tothe liquid state (as represented in FIG. 2E, in which the molten blockis represented by reference 214′), and flows away from the device viaappropriate means.

Because of this fact, drain 213 is no longer maintained in contact withcold plate 212 but instead is moved away under the action of spring 215.Because of the displacement of drain 213 and its loss of contact withcold plate 212, equipment item 211 and cold plate 212 are separated bythe thickness (or screen) of air 216, except for spring 215, whosethermal conductivity is negligible, and these two members are thereforesubstantially insulated by means of air screen 216.

According to the embodiment represented in FIG. 2F, the displacement ofdrain 213 then continues until it comes into contact with structuralpart 210, which then in this case could in turn act as a heat sink.

FIG. 3A represents a third exemplary embodiment of the invention undernormal operating conditions.

According to this example, heat-generating equipment item 301 and coldpart 302 acting as cold source are situated respectively in the upperpart and the lower part of a chamber 305.

A space formed in the chamber between equipment item 301 and cold part302 is filled with a bonding material 303 in liquid form having lowthermal resistance, and which forms a heat-conduction path betweenequipment 301 and cold part 302.

Chamber 305 hermetically houses equipment item 301, bonding material 303and cold part 302. Only a safety valve 304 penetrating into the chamberin the space filled with bonding material 303 makes it possible, ifnecessary, to evacuate liquid when the pressure exceeds a threshold, asexplained hereinafter.

Bonding material 303 is such that its vaporization temperaturecorresponds approximately (and preferably is slightly lower) to adesired maximum temperature in cold part 302.

Because of this fact, when the temperature of the bonding materialexceeds the vaporization temperature (and therefore attains the desiredmaximum temperature), for example by reason of a malfunction ofequipment item 301, bonding material 303 passes from the liquid state tothe gas state during a phase represented in FIG. 3B (the material ingaseous form 303′ naturally appearing in the upper part of the space ofchamber 305 previously occupied by the liquid, in contact with equipmentitem 301).

The change of state in hermetic chamber 305 causes a pressure risetherein until the pressure attains the trip threshold of safety valve304, and the liquid part of bonding material 303 consequently begins toescape, as represented in FIG. 3B.

If the temperature continues to rise beyond the vaporization temperatureof bonding material 303, the phenomenon just described and illustratedin FIG. 3B continues until the space of chamber 305 situated betweenequipment item 301 and cold part 302 is completely filled with gas phase303′ of the bonding material.

The heat path initially formed by bonding material 303 in liquid form istherefore interrupted, and by virtue of this fact cold part 302 isthermally insulated from equipment item 301, since the thermalresistance of the bonding material in gaseous form is much greater thanthat of the bonding material in liquid form.

It is noted that the change of phase (or in other words the transitionfrom the liquid state to the gas state) of the bonding material has alsomade it possible to replace the heat path by a gas screen, which makesit possible in particular to prevent the formation of electrical arcsbetween equipment item 301 and cold part 302.

FIG. 4A represents a fourth exemplary embodiment of the invention undernormal operating conditions, or in other words for temperatures(including the normal operating temperature) clearly lower than apermitted maximum temperature.

In this exemplary embodiment, a chamber 405 is formed in the lowerprolongation of a hot plate 401 (which constitutes, for example, part ofan equipment item containing a heat source, such as a fuel pump withwhich the aircraft are equipped).

Chamber 405 is hermetic and its lower part contains, under normaloperating conditions, a liquid component 403.

Part of a heat drain 404 is also accommodated inside chamber 405: anupper part 406 (substantially horizontal in this case) extends over theentire surface (horizontal in this case) of chamber 405, in such a wayas to form a piston separating an upper part of chamber 405, filled withair, for example, from a lower part of chamber 405, filled with liquidcomponent 403 under normal operating conditions.

It can therefore be considered that the drain floats on liquid component403 during normal operation.

Heat drain 404 also comprises a rod (substantially vertical in thiscase), a lower part 407 of which is in contact, during normal operationas illustrated in FIG. 4A, with a cold part forming a heat sink, in thiscase composed of liquid fuel 402 of the aircraft. Lower part 407 in thiscase is precisely immersed in fuel 402 as represented in FIG. 4A.

In the normal operating configuration shown in FIG. 4A (in other words,especially at nominal operating temperature), a heat path is thereforeformed between equipment item 401 and cold part 402 by means ofmaterials having relatively low thermal resistance, namely in this casethe walls of chamber 405, liquid component 403 and heat drain 404.

When the temperature in chamber 405 rises above the nominal operatingtemperature (for example, because of a malfunction of equipment item401) and attains the vaporization temperature of liquid component 403(preferably chosen to be lower than a permitted maximum temperatureinside chamber 405, which corresponds, for example, to a temperaturebeyond which risks exist due to the presence of fuel 402), a gas phase403′ is formed in the lower part of chamber 405, and the pressureexerted thereby tends to displace upward heat drain 404, whose upperpart 406 it is recalled, forms a piston, as represented in FIG. 4B.

Thus the movement of heat drain 404 produced under the effect ofpressure, itself caused by the change of state of liquid component 403,drives the vertical part of the heat drain at least partly beyond coldpart 402, thus limiting the transfer of heat to this cold part andpreventing overheating thereof.

If the temperature nevertheless happens to rise further beyond thevaporization temperature of liquid component 403, this entire componentis transformed to gas and the pressure exerted in the lower part ofchamber 405 rises in such a way that drain 404 is driven upward so farthat its lower part 407 emerges from the fuel forming cold source 402and finishes its travel at a distance from it. In this final position,the space situated between lower part 407 of drain and the surface ofliquid fuel 402 is filled with a thermally and electrically insulatinggas screen (such as air, for example), so that equipment item 401 andliquid fuel 402 forming a cold source are sufficiently insulatedthermally and electrically to avoid any risk of fire from fuel 402.

The foregoing exemplary embodiments are merely possible examples ofimplementation of the invention, which is not limited thereto.

1. A device comprising an equipment item (101; 201; 211; 301; 401) witha heat source, a part (102; 202; 212; 302; 402) relatively colder thanthe equipment item and a member (103; 203; 204; 213; 214; 303; 403, 404,405) capable of transmitting the heat from the equipment item to thecold part, characterized in that the member is such that, under certainthermal conditions situated above a given thermal condition, theequipment item and the cold part are substantially insulated thermally.2. A device according to claim 1, wherein the equipment item and thecold part are substantially insulated electrically, at least under thesaid thermal conditions.
 3. A device according to claim 1 or 2, whereinthe equipment item and the cold part are separated substantially by agas screen (106; 206; 216; 303′), at least under the said thermalconditions.
 4. A device according to one of claims 1 to 3, wherein themember is such that its thermal resistance is capable of increasingunder the said thermal conditions, in such a way that the member becomessubstantially insulating.
 5. A device according to claim 4, wherein themember comprises at least one component (303) whose change of stateunder the said thermal conditions causes the increase of the saidthermal resistance.
 6. A device according to claim 5, wherein the saidchange of state is a transition from the liquid state to the gas state.7. A device according to claim 5 or 6, claim 4 being taken in dependenceon claim 3, wherein the component forms the said screen (303′) after thesaid change of state.
 8. A device according to one of claims 1 to 3,wherein the member (103; 203; 213; 404) is configured to lose contactwith the equipment item or the cold part under the said thermalconditions.
 9. A device according to claim 8, wherein the membercomprises at least one component (103; 204; 214; 403) whose change ofstate under the said thermal conditions causes the said loss of contact.10. A device according to claim 9, wherein the said component (103)participates in conduction from the equipment item to the cold partoutside the said thermal conditions and disappears due to its change ofstate under the said thermal conditions, thus substantially insulatingthe equipment item and the cold part.
 11. A device according to claim 9,wherein the change of a mechanical property of the component (204; 214;403) during its change of state leads to a movement of a part (203; 213;404) of the member, thus causing the said loss of contact.
 12. A deviceaccording to one of claims 9 to 11, claim 8 being taken in dependence onclaim 3, wherein the member is configured in such a way that the changeof state of the component permits the formation of the said gas screen.13. A device according to one of claims 9 to 12, wherein the change ofstate is a transition from the solid state to the liquid state.
 14. Adevice according to one of claims 9 to 12, wherein the change of stateis a transition from the liquid state to the gas state.
 15. A deviceaccording to one of claims 1 to 14, wherein the equipment item is a fuelpump.
 16. A device according to one of claims 1 to 15, wherein the coldpart is a liquid fuel.
 17. A device according to one of claims 1 to 15,wherein the cold part is a member sensitive to temperature elevations.18. An aircraft equipped with a device according to any one of claims 1to 17.